“I used one of those clear dummy cds that can be found at the top and bottom of spindles. I made a 4.5 volt battery pack out of 3 AA’s and used a motor out of a CD player I salvaged. The green sphere is hollow (something I saved last Christmas, thinking I’d find a use for it ) and is made of two sides which fit together. I mounted the battery pack in one side of the sphere and the motor (with it’s shaft sticking through a hole I drilled in it) on the other. I wired the battery pack to the motor, added a switch and attached the two sides back together. I then used hot glue to fit the dummy cd on the shaft of the motor. The motor spins the contents of the green sphere at about 300 RPM, or about 5 rotations a second. It is amazing watching it defy gravity and vibrate around on the floor. It balances on the edge of the disc, which is a very small footprint.” – Link.